Production of artificial threads



March 14, 1961 w N T 2,975,024

PRODUCTION OF ARTIFICIAL THREADS Filed Jan. 21, 1959 Wm lglll I III III

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//7|//7f0r A/ber/ Wa/fer 86/7/76 By his alfameys States Patent Qfice PRODUCTION OF ARTIFICIAL THREADS Albert Walter BennettyCoventry, England, assign'or to Courtaulds Limited, London, England, a British com- P y Filed Jan. 21, 1959, Ser. No. 788,120

Claims priority, application Great Britain Feb. 18, 1958 3 Claims. (Cl. 1854) This invention relates to the production of artificial threads, fibres, filaments, staple fibres, ribbons, films and the like, hereinafter referred to generally as threads, and is particularly concerned with the production of threads of polyacrylonitrile which term as used in this specification includes simple polymers of acrylonitrile and copolymers containing at least 80 percent of acrylonitrile in the molecule together with up to 20 percent of one or more other unsaturated compounds which are so-polymerisable with acrylonitrile such as styrene, methyl acrylate and vinyl acetate, or dyeable additives such as a vinyl pyridine.

It is known that polyacrylonitrile can be dissolved in concentrated aqueous and aqueous alcoholic solutions of metal salts such as sodium thiocyanate, calcium thiocyanate and zinc chloride and that threads can be obtained from such solutions by wet spinning processes using water or aqueous salt baths as coagulant. The present inven tion provides an improved process for wet spinning such salt solutions of polyacrylonitrile which considerably simplifies the recovery of the salt from the coalgulant bath.

In accordance with this invention a process for the production of polyacrylonitrile threads comprises extruding downwards a solution of polyacrylonitrile as defined in a concentrated salt solution in a co-currently moving stream of an aqueous coagulant, the rate of feed of which is adjusted so that a liquid-liquid interface is formed and maintained in the coagulant stream, and withdrawing the freshly coagulated thread so formed from the coagulant stream at a point below the interface.

The present invention employs the principle in wet spinning generally referred to as tube spinning in which -a thread-forming solution is extruded into a tube containing moving coagulating liquid. In this invention, the tube containing the coagulant is arranged vertical or nearly vertical and the polyacrylonitrile solution is extruded downwards from a jet into the coagulant which is fed in near the top of the tube and so is also moving downwards. The coagulant is fed into the tube at a controlled rate to form a liquid-liquid interface in the manner described below.

The coagulant used may be either water or a dilute aqueous solution of the salt which is present in the spinning solution. A convenient dilute salt solution for use as coagulant is the wash liquor which is obtained at the subsequent operation of washing the threads free from the salt used in the polyacrylonitrile solvent, the liquor containing usually about 0.5-2'percent of the salt.

The coagulation of threads formed by extrusion of a concentrated salt solution of polyacrylonitrile into an aqueous bath proceeds by 'diifusion of aqueous salt from the freshly-formed filaments into the coagulation liquor. The aqueous salt which diiiuses out in the early stages of coagulation has a higher density than the surrounding coagulation liquor and thus tends to fall away from the filaments under the action of gravity towards the bottom of the tube. Under the vertical spinning conditions of this invention using water or dilute salt solution as co- Patented Mar. 14, 1961 agulant it has been observed that coagulation in the early stages takes place in very dilute solution and a distinct interface between two liquid phases can be clearly seen. The lower phase which exists at a small but definite distance from the face of the jet has a high salt content and the upper phase has a muchlower concentration. The actual distance of the interface from the jet depends on a number of factors, including the volume of input of the coagulant liquid and, in general, the input should be so arranged that there is little or no turbulence in'the tube as, otherwise, the interface would tend to disappear and the gravitational separation of concentrated solution would be hindered.

This invention is applicable to the spinning of polyacrylonitrile solutions in concentrated aqueous or aqueous alcoholic salt solutions of such salts as sodium thiocyanate', calcium thiocyanate, ,zinc chloride, lithium chloride and the like. Aqueous alocholic salt solutions for example the solutions described in British patent specifications Nos. 714,530 and 768,708 and also the solutions obtained by solvent polymerisation or copolymerisation of acrylonitrile in thiocyanate solution as described and claimed in the specification of Schmidts application Serial No. 608,706, now Pat. No. 2,923,694, may be used.

The process of this invention compared with the more usual horizontal spinning process into a large volume coagulant bath requires lower volumes of coagulation liquors and, as the liquor withdrawn from the base of the tubes is of relatively high concentration, recovery of the salt is considerably facilitated. The recovery process is also made more economical particularly when wash liquors are used as coagulant liquors.

-In a preferred method of carrying out this invention, the jet is surrounded by a tube, for example of glass, having a small hole in the base. Coagulant liquor is fed in at thetop of the tube at a point just above the jet so that it flows down the tube with the freshly-formed thread and then passes out with it through the. small hole. The tube is maintained full of liquor by providing an airtight seal at the top and pre-selecting the. size of the hole in the base of the tube.

A suitable spinning apparatus is shown in the accompanying drawing which is a vertical section through the apparatus.

Referring to the drawing a glass spinning cell 1 having a flanged rim 2 at its upper end and narrowing to a neck 3 at its lower end is closed at its upper end by a gasket 4 and a steel plate 5 placed symmetrically over the flanged rim 2. The plate 5 and gasket 4 are clamped on the flanged rim 2 by bolts 6 in the plate 5 screwed into a clamping ring 7 which surrounds the cell 1. The neck 3 is constricted by adjustable shutters 8 held between fixed plates 9 and 10, the shutters defining the aperture 11. Through the plate 5 and gasket 4 a coagulant liquor supply line 12, a liquor release valve 13, a thermometer 14 and a spinning solution supply line 15 enter the spinning cell 1. Within the cell a jet 16 is mounted in a jet holder 17 which is secured on the spinning solution supply line 15.

In practice the polyacrylonitrile solution is extruded through the jet 16 into the spinning cell 1 containing coagulant liquor supplied by the supply line 12, the thread 18 and some diluted solvent being withdrawn through the denser diluted solvent from the coagulated spinning solution a liquid-liquid interface 19, below the level of the jet 16. The thread issuing from the cell 1 is led away to be processed and the effluent liquor from the cell is returned to a solvent recovery plant.

The operation of the spinning apparatus is illustrated by the following examples.

Example 1 A solution of 12.5 parts of a copolymer containing 94 percent of acrylonitn'le and 6 percent of methyl acrylate in 87.5 parts of 51.5 percent by weight aqueous sodium thiocyanate was extruded at the rate of 420 cc. per minute through a downward facing jet containing 10,000 holes of 0.003 inch diameterinto a spinning cell. Coagulant liquor 1 percent by weight aqueous sodium thiocyanate) at 17 centigrade was introduced'into the spinning cell at the rate of gallons per hour above the jet. The coagulated thread was withdrawn from the spinning cell by rollers at the rate of i 3.5 metres per minute, stretched 750 percent,- washed and dried. The liquor flowing from the spinning cell with the tow was collected and passed to an evaporator in which the concentration was raised to 51.5 percent by weight of aqueous sodium thiocyanate.

The liquor in the spinning tube separated into two phases with an interface below thejet face. The upper phase was 1.26 percent by weight aqueous sodium thiocyanate, whilst the lower, as passed to the evaporator was 14 percent by weight aqueous sodium thiocyanate.

Example 2 In an identical apparatus to thatused in Example 1, the flow of coagulant was increased to 22 gallons per hour when the, concentrations above and below the interface were respectively 1.22 percent and 11.0 percent by weight aqueous sodium thiocyanate.

The process described in the examples may be applied to solutions of other polymers or copolymers of acrylonitrile, for example a ternary polymer of acrylonitrile, methyl acrylate and vinyl pyridine, containing at least 80 percent of acrylonitrile, and may also be applied to solutions of polymers in concentrated solutions of other salts such as calcium thiocyanate or zinc chloride.

What I claim is:

1. A process for the production of threads from polymeric materials selected from the group consisting of simple polymers of acrylonitrile and copolymers containing in the molecule at least percent of acrylonitrile and up to 20 percent of at least one other unsaturated compound which is copolymerizable with acrylonitrile, which process comprises extruding downwardly said polymeric material dissolved in a concentrated solution of a salt selected from the group consisting of sodium thiocyanate, calcium thiocyanate, zinc chloride and lithium chloride, into a cocurrently moving stream of a coagulating solution, the rate of flow of said stream being adjusted to maintain aliquid-liquid interface in said stream between an upper liquid having a concentration of said salt not greater than about 2% and a lower liquid having a concentration of said salt of at least about 11%, and withdrawing freshly coagulated thread from the coagulating solution.

2. A process as claimed in claim 1 in which the concentrated salt solution is an aqueous salt solution.

3. A process for the production of threads from polymeric materials selected from the group consisting of simple polymers of acrylonitrile and copolymers containing in the molecule at least 80 percent of acrylonitrile and up to 20 percent of at least one other unsaturated compound which is copolymerizable with acrylonitrile, which process comprises extruding downwardly said polymeric material dissolved in a concentrated solution of sodium thiocyanate into a cocurrently moving stream of a coagulating solution, the rate of flow of said stream being adjusted to maintain a liquid-liquid interface in said stream between an upper liquid having a concentration of sodium thiocyanate not greater than about 2% and a lower liquid having a concentration of sodium thiocyanate of at least about 11%, and withdrawing freshly coagulated thread from the coagulating solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,733 Cresswell July 3, 1951 2,777,751 Cresswell Jan. 15, 1957 FOREIGN PATENTS 737,937 Great Britain Oct. 5, 1955 

1. A PROCESS FOR THE PRODUCTION OF THREADS FROM POLYMERIC MATERIALS SELECTED FROM THE GROUP CONSISTING OF SIMPLE POLYMERS OF ACRYLONITRILE AND COPOLYMERS CONTAINING IN THE MOLECULE AT LEAST 80 PERCENT OF ACRYLONITRILE AND UP TO 20 PERCENT OF AT LEAST ONE OTHER UNSATURATED COMPOUND WHICH IS COPOLYMERIZABLE WITH ACRYLONITRILE, WHICH PROCESS COMPRISES EXTRUDING DOWNWARDLY SAID POLYMERIC MATERIAL DISSOLVED IN A CONCENTRATED SOLUTION OF A SALT SELECTED FROM THE GROUP CONSISTING OF SODIUM OF OCYANATE, CALCIUM THIOCYANATE, ZINC CHLORIDE AND LITHIUM CHLORIDE, INTO A COCURRENTLY MOVING STREAM OF A COAGULATING SOLUTION, THE RATE OF FLOW OF SAID STREAM BEING ADJUSTED TO MAINTAIN A LIQUID-LIQUID INTERFACE IN SAID STREAM BETWEEN AN UPPER LIQUID HAVING A CONCENTRATION OF SAID SALT NOT GREATER THAN ABOUT 20% AND A LOWER LIQUID HAVING A CONCENTRATION OF SAID SALT OF AT LEAST ABOUT 11% AND WITHDRAWING FRESHLY COAGULATED THREAD FROM THE COAGULATING SOLUTION. 